1 Simulation of a DS/SS System Using MATLAB-Simulink W. A. Mahmoud, Hikmat N. Abdullah and J. M. Al-Samarei University of Baghdad, University of Technology اﻟﺨﻼﺻﺔ ﺎѧﺎؤهϨΑ ϢѧΗ ﺮةѧηﺎΒϤϟ اﺔѧόΑﺎΘΘϤϟﺎΑ ﺮθѧΘϨϤϟ اϒѧϴτϟ اتϻﺎμѧΗ اﺔѧϣﻈﻮϨϤϟ ϒѧλ وﺚΤΒϟ ا هﺬاϲϓ Βϟ اﺨﺪامΘγﺎΑ Ξϣﺎϧ ﺮ.MATLAB-Simulink ﺪةѧΣ وﺎءѧϨΒϟ ﺔѧϘϳﺮσ ﺮاحΘϗ اϢΗ ϩϼϋ أﺔϣﻈﻮϨϤϟ اϲϓ ﺚΤΒϟ اﺮةτϴγ / ϦϣﺰاΘϟ اﺔϠΣﺮϣ ϦϤο ϞϔϘϟ ا. ϖϳﺎدϨѧλ ﺨﺪامΘѧγ اϢѧΗ ﺪѧϗ و أدواتتϻﺎμѧΗϻ اﺔѧΠϟﺎόϣ و ﺎرةѧη اﻹﺔϤδѧϘϤϟ اﺮةϔθѧϟﺎΑ ﺪدѧόΘϤϟ ا ﻮلѧλﻮϟ وا ﺔѧϴϤϗﺮϟ اﺔϓ ﺎѧοﺎﻹΑ ﺔϴϓ ﺎѧο اﻹ اﻷدواتﺪوقϨѧλ ﻰѧϟ إ ΞϣﺎѧѧϧﺮΑ ϦϤѧѧο ﻮدةѧѧΟﻮϤϟ ا.MATLAB-Simulink ϢѧѧΗ ، ﺬآﻮرةѧѧϤϟ اﺔѧѧϣﻈﻮϨϤϟ اﺎءѧѧϨΑ ϢѧѧΗ أنﺪѧѧόΑ ϊϳﻮزΗ ذاتﺔϓﺎπϣ ﺎءπϴΑ ﺎءοﻮο ﻮدΟﻮΑ وﺎحΠϨΑ أداﺋﻬﺎϞϴϠΤΗ وﻬﺎμΤϓ ﺔϴϟﺎϤΘΣ ا آﺎوس. Abstract This paper presents the description and implementation of a direct sequence spread spectrum (DS/SS) system using MATLAB-Simulink. A search/lock control unit (SLCU) is proposed to control the operation of synchronization subsystem. Toolboxes from communication blockset, DSP blockset, CDMA blockset and Simulink-Extras are employed. The simulated system is tested, evaluated and its performance is obtained in the presence of additive white Gaussian noise. I-Introduction Spread spectrum systems have played an outgrowing role in modern communication systems for both military and civil applications due to many reasons such as anti-jamming, anti-interference, low probability of intercept, multiple user random access communication and high resolution ranging [1]. Spread spectrum systems are most favorable for indoor communication needs [2] and digital radio links [3] where most of the applications are found. Fig.1 shows the functional block diagram for a binary phase shift keying modulated (BPSK) direct sequence system. The binary data is modulo-2 added with a pseudo-random spreading signal before being phase modulated. At the receiver, a phase shift modulated waveform is multiplied by a locally generated pseudo-random sequence identical to that used in the transmitter to encode the modulation. At receiver, the spread spectrum signal can be represented by [4]: ) 1 ( ) ( ) cos( ) ( ) ( 2 ) ( 0   t n t t c t d S t      